Recently, brushless direct current motors (BDCMs) have been the subject of much work and discussion. The stator windings of these motors are sequentially energized at appropriate times to produce a rotating magnetic field, which in turn causes rotation of the motor's permanent magnetic rotor.
Control devices for BDCMs have conventionally used full-wave bridge inverters having six solid state switching devices and six diodes to appropriately switch a single DC source of power to provide three-phase energization of the stator windings of BDCMs (see for example, U.S. Pat. No. 4,544,868 issued Oct. 1, 1985 to Murty, and assigned to the same assignee as the present application).
When BDCMs are used as a means for propulsion in electric or hybrid vehicles, the capacity of the motors and inverters must be substantial due to the large power requirements. In such applications, the inverters can represent a significant portion of the cost, mass, and packaging size of the motor propulsion systems. In addition, the reliability of control devices using such inverters is inversely related to the required number of solid state switching devices and diodes in the inverter.
Accordingly, it would be advantageous if fewer solid state switching devices and diodes could be employed in the fabrication of power inverters in control devices used for driving BDCMs.